Nesidioblastosis is a term used to describe histologic changes in the pancreatic cell, which are defined by beta cell hypertrophy and the formation of ductoinsular complexes. It is a disease previously most extensively identified in neonates and is a rare cause of endogenous hypoglycemia in the adult population. However, with increasing numbers of gastric bypass surgeries for the management of obesity in recent years, there has been a growing number of populations with post-gastric bypass surgery-related nesidioblastosis. Here, we will present a case of a 60-year-old female with a history of Roux-en-Y gastric bypass (RYGB) surgery who initially presented with loss of consciousness and episodes of suspected hypoglycemia. Insulinoma was ruled out, supporting the diagnosis of adult onset RYGB-associated nesidioblastosis.This article was previously presented as a poster presentation at the 2023 Research Symposium, International Conference on Health Disparities, on September 8, 2023.

Differential diagnosis of hypoglycemia in the non-diabetic adult patient is complex and comprises various diseases, including endogenous hyperinsulinism caused by functional β-cell disorders. The latter is also designated as nesidioblastosis or non-insulinoma pancreatogenous hypoglycemia syndrome (NIPHS). Clinically, this rare disease presents with unspecific adrenergic and neuroglycopenic symptoms and is, therefore, often overlooked. A combination of careful clinical assessment, oral glucose tolerance testing, 72 h fasting, sectional and functional imaging, and invasive insulin measurements can lead to the correct diagnosis. Due to a lack of a pathophysiological understanding of the condition, conservative treatment options are limited and mostly ineffective. Therefore, nearly all patients currently undergo surgical resection of parts or the entire pancreas. Consequently, apart from faster diagnosis, more elaborate and less invasive treatment options are needed to relieve the patients from the dangerous and devastating symptoms. Based on a case of a 23-year-old man presenting with this disease in our department, we performed an extensive review of the medical literature dealing with this condition and herein presented a comprehensive discussion of this interesting disease, including all aspects from epidemiology to therapy.

BACKGROUND: Hyperinsulinemic hypoglycemia is the most common cause of severe and persistent hypoglycemia in neonates and children. It is a heterogeneous condition with dysregulated insulin secretion, which persists in the presence of low blood glucose levels.
METHODS: We report a case of a 15 year-old male with hyperinsulinemic hypoglycemia, who underwent a subtotal pancreatectomy after inadequate response to medical therapy. Pathological examination was positive for nesidioblastosis (diffuse β-cell hyperplasia by H-E and immunohistochemical techniques). The patient\'s blood glucose levels normalized after surgery and he remains asymptomatic after 1 year of follow-up. The systematic review allowed us to identify 41 adolescents from a total of 205 cases reported in 22 manuscripts, from a total of 454 found in the original search done in PubMed and Lilacs.
CONCLUSIONS: Although very well reported in children, hyperinsulinemic hypoglycemia can occur in adolescents or young adults, as it happens in our reported case. These patients can be seen, treated and reported by pediatricians or adult teams either way due to the wide age range used to define adolescence. Most of them do not respond to medical treatment, and subtotal distal pancreatectomy has become the elected procedure with excellent long-term response in the vast majority.

Hypoglycemia due to endogenous hyperinsulinism usually occurs in 2 pathological situations: the most frequent is insulinoma and, secondly, nesidioblastosis or also known as non-insulinoma pancreatic hypoglycemic syndrome. Nesidioblastosis is a rare cause of hyperinsulinic hypoglycemia in adults. We present the clinical case of an adult patient with recurrent hypoglycemia secondary to nesidioblastosis.
La hipoglucemia por hiperinsulinismo endógeno suele presentarse en dos situaciones patológicas: la más frecuente es el insulinoma y, en segundo lugar, la nesidioblastosis o síndrome hipoglucémico pancreático no insulinoma. La nesidioblastosis es una causa poco frecuente de hipoglucemia por hiperinsulinismo en adultos. Presentamos el caso de un paciente adulto con cuadros recurrentes de hipoglucemia secundarios a nesidioblastosis.

BACKGROUND Nesidioblastosis is a rare disease that is part of the differential diagnosis of pancreatogenic hyperinsulinemic hypoglycemia (PHH) in patients whose imaging studies do not localize insulinoma. Pancreatic heterotopia is a rare congenital abnormality characterized by pancreatic tissue anatomically separated from the main gland and found in 0.5% of abdominal surgeries. The purpose of this article is to provide a systematic review of the literature on nesidioblastosis in pancreatic ectopic tissue and to describe a case of the co-occurrence of these 2 rare conditions. CASE REPORT A 32-year-old man presented with adrenergic and neuroglycopenic symptoms, with laboratory-confirmed hyperinsulinemic hypoglycemia. There was no evidence of tumors on abdominal CT scan and MRI. Celiac trunk sampling with a calcium stimulation test was done, which showed an insulin gradient in the gastroduodenal artery. However, the intraoperative ultrasound showed a small nodule located at the pancreatic tail, leading to distal pancreatectomy. The histologic examination showed nesidioblastosis associated with pancreatic heterotopia. The patient remained asymptomatic after distal pancreatectomy. CONCLUSIONS Nesidioblastosis accounts for 0.5%-5% of all cases of PHH, with a histology showing hypertrophy and hyperplasia of pancreatic islets. Pancreatic heterotopia is a rare congenital anomaly resulting from failure of pancreatic cell migration, and is found as an incidentaloma in imaging or surgeries. Although it is a rare disease, nesidioblastosis should be considered in the investigation of hypoglycemia, even in the rare presentation of nesidioblastosis in patients with pancreatic heterotopy.

Nesidioblastosis is an uncommon cause of organic persistent hyperinsulinemic hypoglycemia in adults. We report a case of adult-onset diffuse β-cell nesidioblastosis in a 49-year-old woman who was status-post Roux-en-Y gastric bypass and distal pancreatectomy for a well-differentiated pancreatic neuroendocrine tumor. While the neuroendocrine tumor was suspected to be an insulinoma, persistent hypoglycemia postoperatively suggested either incomplete resection or a second pancreatic neoplasm. Completion pancreatectomy revealed islet β-cell hyperplasia and nuclear pleomorphism consistent with β-cell nesidioblastosis. The patient\'s blood glucose levels normalized after completion pancreatectomy. While β-cell nesidioblastosis and insulinomas can coexist in the same patient, pathologists should be aware of β-cell nesidioblastosis as a potential cause for hyperinsulinemic hypoglycemia and should exclude it in patients who have not shown definitive clinical response after surgical excision of a pancreatic neuroendocrine tumor.

Congenital and adult-onset hyperinsulinism (CHI) must be taken under consideration in the differential diagnosis of hypoglycaemia symptoms with endogenous hyperinsulinism, especially in cases in which there was failure to find an insulinoma. Histological examination is necessary for a definitive diagnosis. CHI is a disorder with three histopathological variants: focal CHI, diffuse CHI, and atypical CHI. These variants are clinically indistinguishable. According to published statistics, 0.5 to 5% of nesidioblastosis cases occur in adults. Clinical manifestation ranges from mildly symptomatic up to life-threatening hypoglycaemia. Early diagnosis and treatment are important in young and very young patients because early treatment accounts for favourable mental outcomes.

Congenital hyperinsulinism (HI) is characterized by profound hypoglycemia caused by inappropriate insulin secretion. HI is a heterogeneous disorder with at least two histologic lesions and several implicated genes. If HI is caused by a focal lesion, elective surgery is the treatment of choice because it leads to complete recovery without diabetes. On the contrary, near-total pancreatectomy though recommended for diffuse HI, long-term risks of endocrine and exocrine deficiencies are present. Between the years 2006-2011, three patients of HI were referred to and operated by a single surgeon. The preoperative diagnosis was confirmed by recurrent hypoglycemia, inappropriately high insulin levels, and augmented glucose requirements. The medical records of all three patients were reviewed to study their clinical features, medical and surgical treatment, and postoperative outcome (short- and long-term). There were three patients in this series (male/female ratio, 1:2), all presenting in the neonatal age. All patients failed medical treatment, and radiological imaging did not reveal any pancreatic lesion. All patients underwent subtotal (80 %) pancreatectomy. Two patients had diffuse type of HI and one focal HI. One patient had transient hyperglycemia for 3 months, which needed insulin supplementation. No patient has developed recurrent hypoglycemia, malabsorption syndrome, or any neurological sequelae until the last follow-up. Doing subtotal or near-total pancreatectomy in diffuse type of HI still remains controversial as one has a higher risk of recurrent hypoglycemia, while the other has a higher rate of insulin dependent diabetes mellitus. Subtotal (80 %) pancreatectomy may be considered as the primary modality of surgical intervention in diffuse type of HI, especially when the diagnostic facilities are limited or diagnosis is not known after preliminary investigations. This minimizes the chances of postoperative diabetes mellitus, and redo surgery can always be considered if there is recurrent hypoglycemia.

Mediastinal teratomas with elements of mature pancreatic tissue are rare. Only a very few cases of pancreatic tissue with nesidioblastosis in teratoma have been reported. Here, we report a case of a 12-year-old male who presented with pleural effusion and was revealed to have a large anterior mediastinal mass. Biopsy of the mass revealed benign mature teratoma. After biopsy, the teratoma ruptured into the right thoracic cavity. It was then excised and sent to pathology for further evaluation. Preoperatively, there was no evidence of hyperinsulinemia or hypoglycemia. Postoperatively, there was no change in blood glucose levels. Histologically, the mass showed large areas of mature pancreatic tissue flanking a small intestine-like structure. Numerous endocrine cell islets, poorly defined groups of neuroendocrine cells and ductular-insular complexes characteristic of nesidioblastosis were dispersed in the exocrine pancreatic parenchyma. In addition, other parts of the tumor containing keratinizing squamous epithelium with cutaneous adnexal glands, small intestine, and bronchus including cartilage and respiratory epithelium were observed. Some islets contained two or more cell types while others were monophenotypic. Immunohistochemical staining showed pronounced expression of pancreatic polypeptide, moderate expression of somatostatin and insulin and nearly complete absence of glucagon-containing cells. The selective deletion of glucagon might hold clues to an important regulatory mechanism in pancreatic development.

Gastric bypass is one of the most efficient strategies for long-term weight loss and reduction of the comorbidities associated with morbid obesity. Of the complications secondary to gastric bypass, hypoglycaemic episodes have so far been poorly studied. The present study is a comprehensive report of the fewer than 100 cases described in the literature. It shows that strict diagnostic criteria should be applied to differentiate true intense neuroglucopenic symptoms associated with low glucose values (<2.8 mmol/L) from the more frequent symptoms of the dumping syndrome and those occurring in the context of lower-than-normal plasma glucose concentrations. The pancreatic beta-cell hyperfunction initially deemed responsible for hypoglycaemic episodes because of frequent islet abnormalities is described and reappraised in this report. The few validated therapeutic options are also discussed.